Quality and Safety of Soybean Oils in Makurdi: Physicochemical Properties, Contaminants, and Residues

The study aimed to investigate the physiochemical properties, heavy metals, total aflatoxins, and solvent residues in soybean oils produced in some parts of the Makurdi metropolis. The oil samples were collected from “Seraph” and “Hule and Sons” vegetable oil factories in Makurdi. Samples include: Seraph crude soybean oil (A1), Seraph Refined soybean oil (A2), Hule and Sons crude soybean oil (B1), and Hule and Sons refined soybean oil (B2). Analysis showed that the physicochemical properties varied between the refined and unrefined samples. Specific gravity increased from 0.807 to 0.923, 0.822 to 0.931 for A1 and A2 and B1 and B2 respectively. The peroxide value reduced from 9.71 to 9.6 (mEq.O2kg-1) after refining. Iodine value and moisture content also reduced with refining. Cadmium, arsenic, and lead were detected only in the crude soybean oil (A1 and B1) copper content reduced from 5.3 to 2.6 mg/kg, and nickel decreased from 0.55 to 0.01 mg/kg upon refining. Crude soybean oil content (A1 and B1) total aflatoxins of 6.05 ppm and 7.10 ppm respectively. No aflatoxin was detected in the refined oil samples. Major chemical compounds and solvent residues in refined soybean oil (A2) composed of 21.10% 2,4–Decadienal, 18.16% n-Hexadecanoic acid, 4.66% Bicyclo [3.1.1] heptane, 4.45% 1,6,10,14–Hexadecatetraen-3-ol, 4.17% p-xylene, 4.22% cyclohexane, 5.05% cyclopentane, 1.69% 9-Eicosyne and 3.88% toluene. While B2 composed mainly of 2,4-decadienal (27.92%), 2-pentene (17.42%), Bicyclo [3.1.1] heptane (2.10%), 9-octadecyne (1.45%), 2-methyl-E-7-octadecane (1.31%), 2-Heptenal (2.17%), Cyclohexane (2.33%) and Hexanal (2.90%). Refining has a significant role in the physicochemical properties of soybean oil. Refining greatly reduces heavy metal content and aflatoxin in crude vegetable oils.